A suffragan of Compostela, includes nearly all of the civil Province of Orense, and part of those of Lugo and Zamora, being bounded on the north by Pontevedra, Lugo, and Leon; on the east by Leon and Zamora; on the south by Portugal; on the west by Portugal and Pontevedra. Its capital, Orense (pop., 14,168), is a very ancient city on the banks of the Miño (Minho), famous since classical antiquity for its hot springs. The See of Orense dates from a remote period,, certainly before the fifth century. The First Council of Braga (561) created four dioceses, the bishops of which afterwards signed the acts of the Second Council of Braga below the Bishop of Orense - an indication that they were of junior standing. Moreover, the signatures of the Bishops of Tuy and Astorga, two very ancient Churches, come after that of the Bishop of Orense. According to Idacius, two bishops, Pastor and Siagrius, were consecrated in the convent of Lugo in 433, and one of them (it is not known which) was a Bishop of Orense.

In 464, the Suevians, who had invaded Galicia embraced Arianism, and only in the time of King Chararic (560) were they reconciled to Catholicism. St. Gregory of Tours tells us that the Galiciana embraced the Faith with remarkable fervour. The conversion and instruction of both king and people appear to have been completed by St. Martin of Dumium. The names of the bishops of Orense are unknown until 571, when the diocese was governed by Witimir, a man of noble Suevian lineage, who assisted at the Second Council of Braga. He was an intimate friend of St. Martin of Braga, who dedicated to him as his "most dear father in Christ" his treatise "De ira". In 716 Orense was destroyed by Abdelaziz son of Muza. In 832 Alfonso II combined the two Dioceses of Orense and Lugo: Orense, nevertheless, appears to have retained its titular bishops, for a charter of Alfonso the Chaste is witnessed by Maydo, Bishop of Orense. When Alfonso III (866-910) had reconquered Orense, he gave it to Bishop Sebastian, who had been Bishop of Arcabica in Celtiberia and was succeeded by Censerio (844), Sumna (886), and Egila (899), who took part in the consecration of the church of Santiago and in the Council of Oviedo. In the episcopacy of Ansurius (915-22) the holy abbot Franquila (906) erected the Benedictine monastery of S. Esteban de Ribas del Sil (St. Stephen on the Sil), where Ansurius himself and eight of his successors died in the odour of sanctity.

At the end of the tenth century the diocese was laid waste, first by the Northmen (970) and then by Almanzor, after which it was committed to the care of the Bishop of Lugo until 1071, when after a vacancy of seventy years, Sancho II appointed Ederonio to the see. Ederonio rebuilt the old cathedral called S. Maria la Madre (1084-89). The most famous bishop of this period was Diego Velasco, whom his epitaph calls "light of the Church and glory of his country". He assisted at a council of Palencia and three councils of Santiago, and, with the assent of Doña Urraca and her son Alfonso, granted privileges (fueros) to Orense. He ruled for thirty years and was succeeded by Martin (1132-56) and Pedro Seguín. The latter was confessor to Ferdinand II, who granted him the lordship of Orense. Bishop Lorenzo was the jurist whom Tudense called the "pattern of the law" (regla del derecho); he rebuilt the cathedral and the bishop's palace, and constructed the famous bridge of Orense, with its principal arch spanning more than 130 feet. He assisted at the Council of Lyons in 1245. Vañez de Novoa quarrelled with the Franciscans, while he was precenter, and burned their convent, which had sheltered one of his enemies, but, having become bishop, he rebuilt it magnificently. Vasco Perez Mariño (1333-43) was distinguished for his devotion to the "Holy Christ of Orense", which he caused to be transferred from Finisterre to Orense and built for it a beautiful chapel, modified in subsequent periods. Other distinguished occupants of this see were Cardinal Juan de Torquemada, a Dominican, who assisted at the Councils of Constance and Basle; Diego de Fonseca (1471-84), who repaired the cathedral; Cardinals Antoniotto Pallavicino and Pedro de Isvalles, and the inquisitor general Fernando Valdés. Francisco Blanco founded the Hospital of S. Roque, assisted at the Council of Trent, founded the Jesuit colleges at Malaga and Compostela, and endowed that at Monterey. The Zealous Juan Muñoz de la Cueva, a Trinitarian, wrote "Historical Notes on the Cathedral Church of Orense" (Madrid, 1727). Pedro Quevedo y Quintana (died 1818), having been president of the Regency in 1810, was exiled by the Cortes of Cadiz; he founded the conciliar seminary of Orense in 1802.

The original cathedral was dedicated to the Mother of God, and is still known as Santa Maria la Madre. The Suevian king Chararic (see above) built (550) another, more sumptuous, church in honour of St. Martin of Tours and made it the cathedral as it is to this day. Both churches, having suffered severely from time and the invasions of Arabs and Northmen, have been repeatedly restored. The later cathedral is Romanesque, with features of Gothic transition: its oldest portions date from the thirteenth century, and its latest from the early sixteenth; the façade has been rebuilt in modern times. The high altar has a silver tabernacle, given by Bishop Miguel Ares, and statues of Our Lady and St. Martin. In two side altars are the relics of St. Euphemia and her companions in martyrdom, Sts. Facundus and Primitivus. The plan of the church is a Latin cross, with three naves, the tower standing apart. The choir stalls are the work of Diego de Soils and Juan de Auges (late sixteenth century). Of the cloisters only a small portion remains, a perfect gem of ogival work. The church of St. Francis and the Trinity should also be mentioned; it was founded probably about the middle of the twelfth century as a hospice for pilgrims.

The famous men of the diocese include Padre Feijóo, a polygrapher who exploded many superstitions; Antonio de Remesar, the historian of Chiapa and Guatemala; Gregorio Hernandez, the sculptor; Castellar Ferrer, the historian of Galicia; St. Francis Blanco, a martyr of Japan.